This invention relates generally to automatic rearview mirror systems and, more particularly, to such systems incorporating optical display devices within the reflective element in order to display alphanumeric indicators or graphic symbols to the driver.
It has been known to incorporate alphanumeric and graphic displays in vehicle automatic rearview mirror systems. One such example is illustrated in U.S. Pat. No. 4,882,565 issued to W. Gallmeyer for INFORMATION DISPLAY FOR REARVIEW MIRRORS, which is assigned to the assignee of the present application. In the Gallmeyer patent, a plurality of graphic indicia, such as warning signals, are individually displayed near the edge of the reflecting area of the mirror by separately illuminating light emitting diodes (LED) associated with each indicia. Such information displays are also useful for displaying, in either graphic or alphanumeric form, the output of an electronic compass in order to inform the driver of the compass heading of the vehicle. The indicia are etched in the reflective surface of the mirror and a light filter material is provided between the indicia and the light source.
In a copending patent application by Desmond J. O'Farrell and Richard J. Gahan for an ELECTROOPTIC REARVIEW MIRROR WITH LIGHT TRANSMITTING AREA filed on Apr. 27, 1992, Ser. No. 07/874,635, now U.S. Pat. No. 5,253,109, which application is commonly assigned to the present assignee, a portion of the variable reflective element of the automatic rearview mirror, in the vicinity of the display, is maintained in a non-colored state regardless of the state of coloration of the reflective element. In this manner, the intensity of the display placed behind the variable reflective element, as viewed by the driver, is not affected by the light transmission level, or transmissivity, of the electrochromic cell.
It is known to vary the intensity of automobile electronic display systems between a first intensity level for bright ambient light conditions and a second intensity level for dark ambient light conditions. Such intensity variation may be performed by varying the ratio between on and off conditions, or duty cycle, of the display, provided that the switching is sufficiently fast to avoid perception by the human eye. In U.S. Pat. No. 4,388,558 issued to Mizuno et al. the display intensity of an automobile electronic display system is switched between such levels by monitoring the switch used to actuate the vehicle headlights in order to respond to changes in ambient light conditions.